Blackphone, the Swiss start-up that's launching a smartphone with encrypted communications, is planning a series of devices around the same idea, one of the company's co-founders said on Monday.

"It's not the only device we will ever do," said Jon Callas during an interview at the Mobile World Congress expo in Barcelona. "There'll be other security and privacy-enhanced mobile devices."

The Blackphone handset, which is being unveiled at the event, goes on sale in June for US$629. It looks like a typical Android smartphone and is based on a security-hardened version of the OS called "PrivatOS." Standard applications include secure calling and text messaging, encrypted file transfer and video chat.

Those communications functions will be based on technology from Silent Circle, a U.S. provider of secure messaging that was founded by Callas and Phil Zimmermann, who is best known as the creator of the PGP public-key encryption system. Zimmermann is working with Callas and executives from Androind-phone maker Geeksphone on the Blackphone.

"It's a phone whose existence is motivated by the need to protect your privacy," said Zimmermann. "Geeksphone knows how to build phones, Silent Circle knows how to protect privacy. We've added in some apps, integrated it all in, tightened the Android settings down and hardened it against attacks."

The secure communications channel is initiated after two devices -- either two Blackphones or a Blackphone and another device running a Silent Circle app -- connect and negotiate encryption keys. That step means communications between the two are encrypted and remain unintelligible to intermediates, including Silent Circle's own servers.

"We don't require that you trust us. Imagine if our servers fell into the wrong hands. What if the NSA confiscated our servers and installed them in Fort Meade, it wouldn't make any difference," said Zimmermann.

While similar communications are possible on a standard Android or iPhone running the Silent Circle app, using a Blackphone means the user doesn't have to worry so much about attacks to the hardware.

"You could just run the app, but then you have to worry about the rest of the platform," said Zimmermann. "For years I've been talking about how it isn't enough to write good crypto, you need a good platform. This is the first time I've been able to work on doing something to protect the platform."

Even before the Blackphone launches, Callas said he's seen a recent uptick in interest in Silent Circle's products. He attributes that to the series of leaks from former government security contractor Edward Snowden.

"It's been great for us," he said of the revelations that have appeared in newspapers since last June. "We have seen direct spikes in sales due to Snowden. Instead of a boutique company, we are now a semi-mainstream company and that is all thanks to Snowden."

Silent Circle's products have always found a user base, said Zimmermann, but the reports on the extent of U.S. and U.K. government surveillance and information sharing are prompting more people to consider privacy.

There remains a gap between complaining about things and actually doing something, but that gap is slowly starting to narrow, said Callas.

The Blackphone handset will be sold direct by the company or through mobile carriers, the only one of which has been announced is KPN Mobile in the Netherlands. The phone has a 4.7-inch screen, 16GB of internal storage, a better-than 2GHz processor and 8-megapixel camera and LTE cellular, according to the provisional specifications.

Included in the price will be a two-year subscription to Silent Circle calling, Disconnect secure search and private browsing and SpiderOak secure file transfer services. Users will be able to gift three contacts a year-long subscription to Silent Circle.